What does « Middle / Center » mean in the Quran?

And thus we have made you a just community that you will be witnesses over the people and the Messenger will be a witness over you. And We did not make the qiblah which you used to face except that We might make evident who would follow the Messenger from who would turn back on his heels. And indeed, it is difficult except for those whom Allah has guided. And never would Allah have caused you to lose your faith. Indeed Allah is, to the people, Kind and Merciful.

Maintain with care the [obligatory] prayers and [in particular] the middle prayer and stand before Allah, devoutly obedient.

Allah will not impose blame upon you for what is meaningless in your oaths, but He will impose blame upon you for [breaking] what you intended of oaths. So its expiation is the feeding of ten needy people from the average of that which you feed your [own] families or clothing them or the freeing of a slave. But whoever cannot find [or afford it] - then a fast of three days [is required]. That is the expiation for oaths when you have sworn. But guard your oaths. Thus does Allah make clear to you His verses that you may be grateful.

The most moderate of them said, "Did I not say to you, 'Why do you not exalt [Allah]?' "

Arriving thereby in the center collectively,